1. Field of the Invention
The present invention relates to an apparatus having a light-emitting element and a method for producing it. More particularly, the invention relates to a light-emitting apparatus which is arranged to be able to control with high precision a quantity of emitted light from a light-emitting element such as a laser diode, and to a photosemiconductor element which can be used to obtain information about motion of a moving object by letting light beam emitted from a light-emitting element such as a laser diode illuminate the moving object and by detecting diffracted or scattered light subjected to phase modulation operation by motion of the moving object, as well as methods for producing such devices.
2. Related Background Art
There are various conventional light-emitting apparatus proposed, in which a light-emitting element such as a laser diode and a light-receiving element such as a photodiode are set in a single casing, a part of a light beam from the light-emitting element is received by the light-receiving element, and a light quantity of emitted outwardly light from the light-emitting element is controlled utilizing output signals from the light-receiving element.
FIG. 1 is a perspective view of major part for the laser diode in such a conventional light-emitting apparatus of this type.
In FIG. 1, reference numeral 1 designates a light-emitting element (laser diode), and 2 a light-receiving element (photodiode), which are mounted on a stem 3 also serving as a heat sink. They are covered with a cap 5 having an exit opening with a transparent glass plate 4, and the inside is filled with inert gas under hermetic seal. Each electrode for light-emitting element or light-receiving element is connected by wire bonding to a lead terminal which is led to the outside.
FIG. 2 and FIG. 3 are cross sectional views as extracted and exploded to show the light-emitting element 1 and the light-receiving element 2 shown in FIG. 1.
In case that the light-emitting element 1 is a laser diode, laser beams are emitted from both ends thereof. One beam 6 thereof is guided to the outside through the glass plate 4 on the package exit opening and is used as a light source. A part of another beam 7 is received by the light-receiving element 2 for a monitor.
Such apparatus is generally used to obtain a constant-power laser beam, generally using a control circuit (APC: Automatic Power Control) for controlling a current in the laser diode such that a quantity of light entering the light-receiving element 2 is always constant.
There are also various proposals for an apparatus in which light from a light-emitting element is made to illuminate an object (moving object) and diffracted or scattered light from the object is detected, whereby information as to the object's movement such as motion or displacement of the object is attained with high precision, for example optical encoders, laser Doppler velocimeters, laser interferometers, and the like. In addition, a variety of apparatuses such as compact disk, magneto-optical disk, CD-ROM, and the like have been proposed for obtaining desired information by making light irradiate an object.
In any of those apparatuses, set in a single casing are the light-emitting element as a light source, the light-receiving element for receiving optical signals and converting them into electric signals, and other optical elements such as lens, beam splitter, mirror, and the like. Since such apparatuses are constructed by assembling separate elements, precise adjustment is necessary for optical position of the elements, which requires much labor and time.
Further, it is expected that the size of each optical element will be further miniaturized in the future. In this occasion, the precision of optical position for each element must be enhanced in proportion to the size reduction.
For example, in Japanese Patent Application Laid-Open No. 62-196880 it is proposed a photosemiconductor apparatus for CD pickup is designed such that the size of entire system is more reduced.
The Japanese Patent Application Laid-Open No. 62-196880 discloses that a laser diode and a prism having a beam splitter function are respectively mounted on a semiconductor substrate on which a light-receiving unit is provided, signal light is guided to return on the same optical path as one through which light from the laser diode is guided to the outside, and the signal light is separated and reflected by the prism to obtain servo signals (signal light).
There have been proposed a variety of conventional production methods of photosemiconductor apparatus in which elements constituting such photosemiconductor apparatus are arranged at high precision on a semiconductor substrate.
An example method is a method in which a spherical collimating lens or the like is provided for a sealing cap of the laser diode, the spherical lens on the cap is aligned with a light-emitting source, and then the lens is fixed.
Japanese Patent Application Laid-Open No. 63-127444 proposes a production method as shown in FIGS. 4A to 4D and FIGS. 5A to 5D.
At the steps in FIGS. 4A and 4B, a light detection element is formed for each of plural chips (11) on a silicon wafer (10). At the step in FIG. 4C, mounted on the silicon wafer (10) are rod chip bars (15) each having a plurality of semiconductor lasers aligned in parallel with the direction perpendicular to the longitudinal direction of the chips (11). Then at the step in FIG. 4D, the silicon wafer (10) is heated to have the chip bar (15) melt-bonded to the silicon wafer. Further at the step in FIG. 5A, rod prisms (16) are bonded onto the light detection elements so as to be in parallel with the chip bars (15). Then the bonded prisms (16) and the silicon wafer is cut together to obtain a plurality of laser couplers at the same time as shown in FIG. 5B. FIG. 5B shows a laser coupler. Each laser coupler is completed after die bonding process and wire bonding one as shown in FIG. 5C and FIG. 5D, respectively.
In these production methods, the size of each optical element used is as small as a square of several mm to less than a square of 1 mm to obtain a smaller photosemiconductor apparatus.
In the laser coupler shown in FIGS. 4A, 4B, 4C, 4D and FIGS. 5A, 5B, 5C, 5D, a prism in the size of about 1.8.times.1.6.times.0.6 mm has functions for bending an output beam from the laser diode and for beam-splitting an input light.